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Nerve Conduction Studies and EMG for Trapped Nerves

Nerve conduction studies and EMG picture

By Mr Ahmed-Ramadan Sadek, Neurosurgeon · 8 min read

🎧 Listen to this guideAudio version coming soon. Narrated in Mr Sadek’s voice using AI voice technology, from a script he has reviewed.

On this page

Key points

  • Nerve conduction studies (NCS) use small electrical pulses on the skin to check how well your nerves carry signals. Electromyography (EMG) uses a very fine needle to record the electrical activity in your muscles. They are often done at the same appointment.[1][3]
  • A spinal surgeon may ask for them to help tell a trapped nerve in the neck or back apart from a problem further down the arm or leg, such as carpal tunnel syndrome, a trapped ulnar nerve at the elbow or a general nerve problem (peripheral neuropathy).[8]
  • The pulses feel like brief taps or small shocks, and the needle like a scratch. You can ask to stop at any time.[3][4]
  • A normal result does not rule out a trapped nerve. EMG picks up only some cases, and signs of nerve damage can take around 2 to 3 weeks to show up, with some sources giving 1 to 4 weeks.[8][9]
  • Results are read alongside your symptoms, examination and MRI, and are sent to the doctor who referred you.[4][5][8]

Go to A&E or call 999 straight away if you have back pain or sciatica together with:

  • Sciatica on both sides.
  • Weakness or numbness in both legs that is severe or getting worse.
  • Numbness around or under your genitals, or around your bottom (anus).
  • New difficulty starting to pee, being unable to pee, or not being able to control when you pee or poo, when this is not normal for you.

These could be signs of a serious back problem that needs to be treated in hospital as soon as possible.[16] See our cauda equina syndrome guide.

What are nerve conduction studies and EMG?

These are two related tests of the nerves and muscles in your arms and legs, carried out in a clinical neurophysiology department.[3]

Nerve conduction studies (NCS). Small sticky pads (electrodes) are placed on your skin. A handheld stimulator then gives a brief electrical pulse over a nerve, and the pads record the response. The test measures how fast, and how strongly, the signal travels along the nerve.[1][4] It is repeated for several nerves.[5]

Electromyography (EMG). A single very fine needle, similar to an acupuncture needle, is placed into a muscle to record its natural electrical activity, at rest and when you tense it.[4][5] No electricity is passed through the needle, nothing is injected and no blood is taken.[4][6]

Doctors often use “EMG” to mean both tests.[4] The NHS says they are usually done at the same time,[1] while one NHS hospital says most of its patients do not need the needle test as well.[6]

Why might a spinal surgeon ask for these tests?

Nerve problems in the neck or lower back can cause pain, pins and needles, numbness or weakness in an arm or leg. So can problems with nerves much further out, in the wrist or elbow, and conditions that affect many nerves at once.[6][8] The symptoms can overlap, and MRI often shows wear and tear that is not causing any symptoms.[8][10]

NCS and EMG can help in several ways:

  • Trapped nerve in the neck or back (radiculopathy). EMG can show which nerve root is affected, how severe the damage is, and whether it is recent or longstanding.[8][12]
  • Carpal tunnel syndrome or ulnar nerve entrapment. A trapped nerve in the neck can sit alongside carpal tunnel syndrome, and conditions at the elbow can mimic a trapped nerve low in the neck. Nerve conduction studies can tell these apart.[8] The NHS says a nerve conduction test may be used if it is not clear that symptoms are carpal tunnel syndrome.[2]
  • Peripheral neuropathy. The tests can pick up a more general nerve problem, such as one linked to diabetes, which may sit alongside a trapped nerve.[1][8]
  • Foot drop. Foot drop is most often caused by an injury to a nerve in the leg, but a slipped disc in the spine is another cause.[15] Nerve tests can help show whether the problem lies at the nerve root next to the spine or further along the nerve.[12]
  • Cervical myelopathy. When the spinal cord in the neck is squeezed, NCS and EMG are useful for ruling out nerve problems in the arms or legs that can cause similar symptoms.[11]

Before the test

Follow your appointment letter. Common advice includes:

  • No creams. Do not put moisturiser, body lotion or oil on your skin on the day, as these interfere with the recordings.[3][4][5]
  • Keep warm. Keep your hands and feet warm, especially in cold weather. Nerves carry signals more slowly when they are cold, which can affect the results.[5]
  • Clothing. Wear loose clothes that roll up easily to your elbows and knees.[3][5][6]
  • Pacemakers and defibrillators. Tell the department in advance.[4][5] Some check with your heart team first.[5] In a small study of 15 people with these devices, routine nerve test pulses did not affect them.[14]
  • Blood thinners. Tell the team if you take any blood-thinning medicine or have a bleeding disorder.[4][6] Hospitals differ: some ask you to keep taking your usual medicines,[4][6] while another says the needle part may not be advisable and may ask you to speak to your GP or specialist.[5] Never stop a blood thinner unless a doctor tells you to.
  • Eating, drinking and medicines. At most units there is no need to fast or stop your usual medicines. Bring a list of what you take.[4][6]

What happens on the day

After questions about your symptoms and history,[4][6] the nerve tests are usually done first, with short pulses along each nerve. If needed, the needle test follows, and you may be asked to tense the muscle being tested.[4][5]

In the UK the electrical nerve tests may be done by a trained healthcare scientist, but only doctors carry out the needle tests, and a doctor looks at the results and writes the report.[3] You can ask for a chaperone.[4][5]

How long does it take?

Estimates vary between departments. One hospital says the nerve conduction part usually takes about 10 to 15 minutes.[6] Another says most appointments take 30 to 45 minutes but advises allowing an hour,[5] and a third says the visit usually takes about 30 minutes but can last around an hour.[4]

How does it feel?

The pulses feel like a sharp tap or a small electric shock. People who have used a TENS machine say it feels similar, and a muscle may twitch.[3][6] Most people find this uncomfortable but manageable.[3] The needle is very thin, and most people feel only a scratch as it goes in.[3][4] If anything is too uncomfortable, tell the tester: the test can be adapted or stopped.[3]

Risks and side effects

Serious side effects are rare.[3][4]

  • Tingling or a brief increase in your usual symptoms for a few minutes after the nerve tests.[3][5]
  • Aching, soreness or a small bruise where the needle went in, usually lasting a short time.[3][4][5]
  • Bleeding into the muscle is rare. One NHS hospital puts significant bleeding complications at less than 1 in 10,000.[4] In a US study, ultrasound scans after the needle test found small bleeds that caused no symptoms in 2 of 101 people on blood-thinning medicine and 1 of 57 on antiplatelet medicine.[13] A review of 370 people who had EMG of the back muscles and a later MRI found no bleeds there.[17]
  • Infection is listed as a possible risk,[6] but the needle is sterile and used only once.[4]

You can go back to normal activities, including driving, straight after the test. One hospital says there is no restriction on testing in pregnancy.[4]

What the results can and cannot show

The tests are very good at confirming a problem when they find one. A review of cervical radiculopathy reported that EMG correctly picks up a trapped nerve in only about 50 to 71 in 100 people who have one, but when it is abnormal it is almost always right.[8] So a normal result does not mean you do not have a trapped nerve.

There are reasons for this:

  • Timing. Muscle changes take time to appear on EMG after a nerve is damaged. A 2025 review says around 14 to 21 days after the pain starts.[8] Another notes the usual guide is 1 to 4 weeks, based almost entirely on animal studies.[9] A test in the first few weeks may be normal.
  • What is measured. In a trapped nerve root, the standard sensory nerve tests are usually normal because the pressure is close to the spine, and the motor nerve tests change only when damage is severe.[8] So most of the information comes from the needle test of the muscles.[12]
  • Matching with MRI. In a Spanish study of 142 people with a suspected trapped nerve in the lower back, nerve tests and MRI agreed in only about 41 in 100. The authors concluded that the two tests look at different things and complement each other.[10]

This is why your specialist will put the result together with your symptoms, your examination and your scan. For scans, NICE advises that imaging for low back pain and sciatica should be considered in a specialist setting only if the result is likely to change management.[7]

Getting your results

You will not usually get results on the day. The recordings are analysed and a report is sent to the doctor who referred you.[3][4][5][6] One hospital aims to do this within 2 weeks, sooner if urgent.[4] That doctor can explain the results alongside your other tests.[3][4]

Your specialist will then explain what the findings mean for you and talk through the options.

When to get help

For emergencies, see the red box above. For back pain, ask for an urgent GP appointment or contact NHS 111 if you feel hot, cold, shivery or generally unwell, or if the pain is severe, starts suddenly or is getting worse quickly.[16] If you are unsure what to do, contact NHS 111. Do not drive yourself to A&E: ask someone to drive you or call 999.[16] If you have pain, swelling or bruising that worries you after the test, contact the department or your GP.[4]

Frequently asked questions

Is an EMG painful?

Usually it is uncomfortable rather than painful, and you can ask to stop at any point.[3][4]

Can I drive home afterwards?

Yes. You can usually drive and get back to normal activities straight away.[4]

Do I need to stop my blood thinner?

Do not stop it on your own. Tell the department beforehand. Many units still do the test, sometimes adapting the needle part; some ask you to speak to your GP or specialist first.[4][5][6]

I have a pacemaker. Can I still have the test?

Usually, yes. Tell the department beforehand, as some check with your heart team first.[4][5][14]

Why was my test normal when I still have symptoms?

EMG misses a fair proportion of trapped nerves, especially early on. It does not mean your symptoms are not real.[8][9]

How soon after my symptoms start should I have the test?

EMG signs of nerve damage usually take around 2 to 3 weeks to appear, and estimates range from 1 to 4 weeks, so very early tests can be normal. Your specialist will decide on timing.[8][9]

Can I have the test if I am pregnant?

One NHS hospital says there is no restriction in pregnancy. Let the department know.[4]

Further reading

References

  1. NHS. Peripheral neuropathy: diagnosis. Page last reviewed 10 October 2022. Link
  2. NHS. Carpal tunnel syndrome. Page last reviewed 17 April 2024. Link
  3. British Society for Clinical Neurophysiology. My EMG (Nerve Conduction and Electromyography). Link
  4. Cambridge University Hospitals NHS Foundation Trust. Nerve conduction studies (NCS) and electromyography (EMG). Approved 26 August 2026. Link
  5. University Hospital Southampton NHS Foundation Trust. Nerve conduction study and electromyogram (EMG). Version 3, June 2022. Link
  6. Robert Jones and Agnes Hunt Orthopaedic Hospital NHS Foundation Trust. Nerve conduction studies (NCS) and electromyogram (EMG). June 2025. Link
  7. NICE. Low back pain and sciatica in over 16s: assessment and management (NG59). Last updated 29 July 2026. Link
  8. Gonçalves LI, Oliveira Junior PH, Baima JPS. Cervical radiculopathy for neurologists: the role of electrodiagnosis. Arq Neuropsiquiatr. 2025;83(10):1-6. Link
  9. Willmott AD, White C, Dukelow SP. Fibrillation potential onset in peripheral nerve injury. Muscle Nerve. 2012;46(3):332-40. Link
  10. Montaner-Cuello A, et al. Comparison of Magnetic Resonance Imaging with Electrodiagnosis in the Evaluation of Clinical Suspicion of Lumbosacral Radiculopathy. Diagnostics (Basel). 2024;14(12):1258. Link
  11. Zileli M, et al. Cervical Spondylotic Myelopathy: Natural Course and the Value of Diagnostic Techniques, WFNS Spine Committee Recommendations. Neurospine. 2019;16(3):386-402. Link
  12. Li JM, Tavee J. Electrodiagnosis of radiculopathy. Handb Clin Neurol. 2019;161:305-316. Link
  13. Lynch SL, et al. Complications of needle electromyography: hematoma risk and correlation with anticoagulation and antiplatelet therapy. Muscle Nerve. 2008;38(4):1225-30. Link
  14. Schoeck AP, et al. Safety of nerve conduction studies in patients with implanted cardiac devices. Muscle Nerve. 2007;35(4):521-4. Link
  15. NHS. Foot drop. Page last reviewed 30 June 2025. Link
  16. NHS. <a href=”https://www.nhs.uk/conditions/sciatica/”>Sciatica</a&gt; (page last reviewed 3 December 2024) and <a href=”https://www.nhs.uk/conditions/back-pain/”>Back pain</a> (page last reviewed 5 March 2026). Link
  17. Gertken JT, et al. Risk of hematoma following needle electromyography of the paraspinal muscles. Muscle Nerve. 2011;44(3):439-40. Link

This article is general information and is not a substitute for advice about your own situation. Please speak to your GP or specialist before making any change to your treatment.

Last checked: October 2026